toupper is a macro which converts lower-case characters to upper case, leaving all other characters unchanged. It is only defined when c is an integer in the range EOF to 255.
You can use a compiled subroutine instead of the macro definition by undefining this macro using `#undef toupper'.
_toupper performs the same conversion as toupper, but should only be used when c is known to be a lowercase character (a--z).### Returns
toupper returns the upper-case equivalent of c when it is a character between a and z, and c otherwise.
_toupper returns the upper-case equivalent of c when it is a character between a and z. If c is not one of these characters, the behaviour of _toupper is undefined.
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**Authoritative source**: BUSMASTER DITA help source `toupper.dita`, compiled into `BUSMASTER.CHM` with the application.
